1. Field of the Invention
The present invention relates to an airbag, to a process of preparing the airbag and to a method of protecting vehicle occupants from unexpected peril during vehicular collision.
2. Description of the Background
A practical trend is to use an airbag system along with seat belts in the construction of current transportation means, especially in automobiles for the purpose of protecting passengers from vehicular collision and its accompanying shock. Since the airbag system is usually installed in the handles or in dashboards of automobiles, the smaller the volume of the airbag, the better. Also, the airbag must have excellent heat-resistance and abrasion-resistance, since it sustains high temperatures and repeated vibrations of the vehicle over a long period of time.
An airbag is structured of a front panel, the driver side panel, the back panel, and the inflator side panel. An inflator adherent hole is positioned in the back panel, and a vent hole can be formed where desired. An inflator adherent hole is a hole by which high-pressure gas is injected into the airbag, and the vent hole is a hole through which high-pressure gas is exhausted from the airbag for the purpose of impact alleviation and suffocation prevention.
In the event of a traffic accident, airbags are required to exhibit several specific properties which include compactness, strength, flexibility and lightness in weight to protect the heads and bodies of passengers. When it comes to an accident, high temperature and high pressure gas from an inflator inflates the airbag in order to protect passengers from any peril. High temperature and high pressure gas generated by the inflator come into contact with the fabric of airbag and the airbag expands. If the airbag fabric is not compact enough, the high temperature and high pressure gas will leakout of the airbag and then touch the human body which may directly cause harmful effects such as suffocation.
The compactness of the airbag fabric is a desirable characteristic. The airbag should have an air permeability less than 0.5 cc/[cm.sup.3 .multidot.second] measured under a 1.27 cm H.sub.2 O pressure difference.
The airbag also needs to exhibit superior tensile strength upon rapid expansion as it is inflated by high temperature and high pressure gas. The tensile strength should be greater than 181 kg/inch, when it is measured by the ASTM D 5034 method. Furthermore, the airbag fabric should have good flexibility and be light in weight in order to increase the efficiency of installation in a module and for lightness of the vehicle. Desirably, the thickness of the airbag fabric should be less than 0.04 cm and the weight of airbag fabric should be less than 250 g/m.sup.2.
Prior art methods of producing fabric for airbags which attempt to satisfy the specific requirements described above are described below.
Japanese Published Patent No. 64-41438 discloses a method of producing airbag fabric using a synthetic filament, whose monofilament denier is less than 3 denier and whose total denier is 840 denier. The monofilament is used in the warp and weft, as the airbag fabric is woven to a warp and weft density of 24 ends/inch. A rubber coating is then applied to the airbag fabric surface.
The coating of an airbag fabric with materials such as chloroprene, neoprene or silicon rubber may improve the compactness of the fabric and the efficiency of hot wind cut-off. Unfortunately, however, the process of production is very complicated and the cost of production consequently increases along with the troublesome problem of re-cycling of airbag fabric. If the compactness of the fabric is too high, there is the additional annoying problem of installing a vent hole in back panel which exhausts high-pressure gas injected into airbag for the sake of alleviating impact and preventing suffocation of driver and occupant.
Japanese Published Patent No. 6-306728 discloses an effort to overcome the problems noted above which result from coating a fabric. Here, some synthetic filament is employed in the warp and the weft which has more than 20 texturing knobs per meter. The denier of the monofilament ranges from 0.6-3.0 denier for the weaving of the airbag fabric. To prevent filling of the warp during weaving, the synthetic filament is textured. This process of preparation, however, has the problem that the compactness of the airbag fabric deteriorates.
Korean Patent Publication No. 92-16632, describes a process of preparing a high-density fabric that uses a synthetic filament, wherein its monofilament denier ranges from about 3.5 to about 4.5 dtex. The fabric has no texturing in the warp and the weft. Though by this process it is possible to improve the compactness of airbag fabric, it is not possible practically to weave a high-density airbag because of filling in the warp during weaving.
In order to eliminate the problem of filling in the warp direction when synthetic filament is used for the warp and the weft, it has been suggested size the warp prior to weaving. This method, however, may result in such problems as increasing the flammability of the fabric and deterioration of several characteristics of the fabric because of the breeding infestation of germs which occurs upon long term storage of the fabric, which bacterial problems result if the fabric is not rid of sizing agent by washing after weaving.
For the purpose of solving the above problems which are incurred during sizing of the warp, it has been suggested to adopt a filament as the warp which has a thicker denier of monofilaments than that of the weft instead of sizing the warp.
Once an airbag is made of uncoated fabric, which has been prepared by the methods described above, the air permeabilities of the back panel and the front panel are likely to be equal. If no vent hole is formed in the back panel of the airbag for the purpose of exhausting high-pressure gas from the airbag, the driver or occupants of a car may be heat injured from the ejected high-pressure gas of the airbag, which is discharged evenly through the back panel, and the front panel. Consequently, there is the troublesome necessity of forming a vent hole in the back panel, if the back panel and the front panel of the airbag are made of uncoated fabric which has the same air permeability.
In order to eliminate the troublesome necessity of forming a vent hole in the back panel of the airbag, when the airbag is made of uncoated fabric, Japanese Published Patent No. 4-281038 describes the following:
a) Prepare fabrics which vary in density by utilizing jacard or the like. PA1 b) Locate low density fabric on the back panel and high density fabric on the front panel for airbag sewing. PA1 (a) providing a woven fabric by weaving polyamide filament of the same density in the warp and weft directions; PA1 (b) forming a low air permeability fabric by heat-setting the above woven fabric at a temperature less than 180.degree. C.; PA1 (c) forming a high air permeability fabric by heat-setting the above woven fabric at 190.degree. C..about.220.degree. C.; and PA1 (d) sewing the high and low air permeability fabric together after locating the low air permeability fabric as the front panel, and the high air permeability fabric as the back panel.
This method has the problem of locating a low density part fabric in the airbag as the back panel, which does not satisfy the strength required of an airbag.
Japanese Published Patent No. 3-27146 and 3-27147 teaches that the air permeability of the front panel is less than that of the back panel of an airbag, wherein the fabric for the airbag is prepared by a Tubular Weave. The fabric is then used as it is in the back panel or the side panel, but it is only used for the front panel after calendering. This method has the problems of complicating the airbag preparation process because of the Tubular Weave and the calendering treatment.